1. Field of the Invention
The present invention relates to modulation of digital data, and more particularly, to a digital data modulating method and apparatus for quickly and accurately determining a code word to be modulated at a boundary between data blocks by using a constraint (d, k) of a run length limited (RLL) code, and a medium for recording a modulated data generated by using the same.
2. Description of the Background Art
In general, in methods for modulating data and recording it in a recording medium, if a signal detected from a recording medium is a binary xe2x80x980xe2x80x99, a non-return-to-zero inverted (NRZI) code indicates that there is no change in a magnetic flux of the recording medium, while if the a signal detected from the recording medium is a binary xe2x80x981xe2x80x99, the NRZI code indicates that the direction of a magnetic flux recorded in the recording medium is transited to the opposite direction, whereby data is recorded onto the recording medium and a recorded signal is detected or reproduced.
The recently used RLL code is an extended code of the NRZI code concept, which converts a 8 bit (1 byte) data to a 16 bit special code (code word). Accordingly, the data recording efficiency is improved as the code word is more densely stored in the recording medium.
For example, since 8 bits entail 256 types of bit combinations, and 16 bits entail 65536 types of bit combinations, the RLL code is generated by converting a 256-bit combination number generated by 8 bits into 256 numbers among the 65536-bit combination number generated by the 16 bits. At this time, the converted data should satisfy the following constraints.
A first constraint is that there should exist a bit having a value of at least one xe2x80x980xe2x80x99 bit among bits having a value of successive xe2x80x981xe2x80x99s.
For example, one data bit is thrice the data recording density stored without any special constraint, and thus, the data is recorded in the recording medium at a high recording density.
In this respect, the first constraint is that even though the data is recorded in the recording medium at a high recording density, it is to be at a distance which enables a magnetic flux polarity of the data bit recorded in the recording medium to be identified.
That is, the first constraint is that the bits having the value of xe2x80x980xe2x80x99 are consecutively recorded in the recording medium, and when the recorded data is reproduced, no interference occurs among the symbols.
A second constraint is to restrict the number of xe2x80x980xe2x80x99s between the xe2x80x981xe2x80x99 bits. The second constraint restores a clock signal from reproduced data by locking a phase locking circuit to the transitions when the data being reproduced are transited.
The RLL code is expressed as (d, k) code, wherein xe2x80x98dxe2x80x99 indicates the minimum number of bits having a value of xe2x80x980xe2x80x99 that is inserted between bits having a value of xe2x80x981xe2x80x99, and xe2x80x98kxe2x80x99 indicates the maximum number of bits having a value of xe2x80x980xe2x80x99 that is inserted between the bits having a value of xe2x80x981xe2x80x99.
For example, (1, 7) code signifies a code which satisfies a constraint in that bits having a value of at least one xe2x80x980xe2x80x99 should exist among the bits having a recorded value of xe2x80x981xe2x80x99, and bits having a value of a maximum of seven consecutive xe2x80x981xe2x80x99s should exist among the bits having a recorded value of xe2x80x981xe2x80x99.
At this time, the bits encoded by satisfying the constraints are modulated to bits having a value of xe2x80x981xe2x80x99 for an edge transited from a high level of the data pulse to a low level or from a low level to a high level, and modulated to bits having a value of xe2x80x980xe2x80x99 for the interval with no pulse transition.
Accordingly, the minimum inverse period of the data pulse is expressed by (d+1)T and the maximum inverse period is expressed by (k+1)T. xe2x80x98Txe2x80x99 indicates a bit time interval in a record data stream. For example, in a (d, k)=(1, 7) code, the minimum inverse period (Tmin) becomes 2T and the maximum inverse period (Tmax) becomes 8T.
The recording density of the data recorded in the recording medium is increased. Thus, in the minimum inverse period (Tmin), since the minimum run (2T) is successively generated, the recorded data stream may include a distortion. That is, a focal factor and normal line slope factors of an amplitude of the 2T wave form output are smaller and more easily dispersed than a focal factor and normal line slope factors of amplitudes of other output wave forms. Thus, when the recorded data is reproduced, an error is easily generated.
When a data signal with an error is modulated, when it is recorded, it becomes a data stream including a DC component. Then, for example, when a drive of the recording medium such as a compact disk is survo-controlled, numerous error signals such as tracking errors easily appear in a form of variation or jitter.
Thus, if possible, the modulated signal should be generated without the DC components. For this purpose, a digital sum value (DSV) is controlled for a source code.
The DSV signifies a value of the sum of the data stream generated after source codes are NRZI-modulated.
A method for recording an audio signal in an optical or a magnetic optical recording carrier and reading it uses an eight-to-fourteen modulation (EFM) or an eight-to-fourteen modulation plus (EFM Plus).
The EFM-modulation signal is a code word generated as a series of 8 bit data words which are converted into a series of 14 bit code words, and 3 bits of merging words are additionally inserted thereto.
That is, each 14 bit code word should satisfy the constraint that bits having a value of xe2x80x980xe2x80x99 have a minimum length (the minimum xe2x80x980xe2x80x99 run length, xe2x80x98dxe2x80x99) of xe2x80x982xe2x80x99, and bits having a value of xe2x80x980xe2x80x99 have a maximum length (xe2x80x980xe2x80x99 run length, xe2x80x98kxe2x80x99) of 10 between bits having a value of the two consecutive xe2x80x981xe2x80x99s. 
In addition, in order to satisfy the constraints between the code words, 3 bits of merging words are used. For example, for a possible total of eight 3-bit merging words, four 3-bit merging words can be used. That is, it may be 001, 010, 000, 100, and the remaining available 3-bit merging words (111,011,101,110) may not be used because they are against the regulation of the k (=2) constraint.
As the merging words are determined according to the regulation, low frequency components can be reduced.
However, in the digital modulating method of the conventional art, even through the input code words are converted into code words by controlling the DSV, the code word is not accurately and quickly modulated into words at a boundary between blocks constructed with the plurality of code words (that is, between the last code word of one block and the first code word of the next block).
Therefore, an object of the present invention is to provide a digital data modulating method that is capable of quickly and accurately determining a code word to be modulated at a boundary between data blocks by using (d, k) constraints of a run length limited (RLL) code, and its apparatus.
Another object of the present invention is to provide a recording medium for storing a digital modulated data by using a digital data modulating method and apparatus that are capable of quickly and accurately determining a code word to be modulated at a boundary between data blocks by using (d, k) constraints of a run length limited (RLL) code.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a digital data modulating method in which the last unit of a block consisting of predetermined units is received and a block is obtained which does not infringe the k-constraint in the RLL code having the (d, k) constraints on the basis of a modulation data table of a predetermined unit.
In the recording medium of the present invention, the last code word of a block consisting of predetermined units is received and units are obtained and stored which do not infringe the k-constraint in the RLL code having the (d, k) constraints on the basis of a modulation data table of a predetermined code word.
To achieve the above objects, there is also provided a digital data modulating method including the steps of: obtaining an ending xe2x80x980xe2x80x99 run length of the last code word of the current block; obtaining a starting xe2x80x980xe2x80x99 run length corresponding to a coding state in which the next block is started; and comparing the total xe2x80x980xe2x80x99 run length generated by adding the ending xe2x80x980xe2x80x99 run length and the starting xe2x80x980xe2x80x99 run length and the pre-set k-constraint, and selecting only a code word satisfying the k-constraint.
To achieve the above objects, there is further provided a digital data modulating method including the steps of: adding a different digital word to an inputted data word and generating a plurality of intermediate sequences; modulating the plurality of intermediate sequences as generated to sequences conforming with the (d, k) constraints according to a pre-set m/n code ratio; and selecting a (d, k) constrained sequence to be recorded in a recording medium, to the exclusion of a (d, k) constrained sequences of xe2x80x980xe2x80x99 run length connected to (d, k) constrained sequences failing to satisfy the k constraint, from the modulated (d, k) constrained sequences.
To achieve the above objects, there is further provided a digital data modulating method including the steps of: adding a different digital word to an inputted data word and generating a plurality of intermediate sequences; modulating the plurality of intermediate sequences as generated to sequences conforming with the (d, k) constraints according to a pre-set m/n code ratio; and selecting a (d, k) constrained sequence to be recorded in a recording medium, to the exclusion of (d, k) constrained sequence having a sub-sequence of xe2x80x980xe2x80x99 run length exceeding a kset value smaller than xe2x80x98kxe2x80x99 used in the modulation process, from modulated (d, k) constrained sequences.
To achieve the above objects, there is further provided a digital data modulating apparatus including: a generator for adding a different digital word to an inputted data word and generating a plurality of intermediate sequences; and a selector for modulating-the plurality of intermediate sequences as generated to sequences conforming to (d, k) constraints according to a pre-set m/n coding ratio, and selecting a (d, k) constrained sequence from modulated (d, k) constrained sequences.
To achieve the above objects, there is further provided a digital data modulating method comprising: a first step in which a different digital word is added to an inputted data word to generate a plurality of intermediate sequences; a second step in which the plurality of intermediate sequences as generated are modulated to sequences conforming with (d, k) constraints according to a pre-set m/n code ratio; and a third step in which a (d, k) constrained sequence is selected to be recorded in a recording medium, to the exclusion of sequences of which xe2x80x980xe2x80x99 run length connected to (d, k) constrained sequences fail to satisfy the k constraint, from modulated (d, k) constrained sequences.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.